Réponse :
1) ABE rectangle en A
BE²=AB²+AE²
BE²=3²+4²
BE=√25=5cm
2) (AB)//(DC)
ED/EA=DC/AB
(4-x)/4 = DC/3
DC=3(4-x)/4
DC = (12-3x)/4=3-0,75x
ED/EA=EC/EB
(4-x)/4 =EC/5
EC = 5(4-x)/4 = (20-5x)/4 = 5-1,25x
3)A = (AB+DC)/2*AD
A =(3+3-0,75x)/2*x
A = (6-0,75x)/2*x
A =(6x-0,75x²)/2 = -0,375x²+3x
4) P DCE = 3-0,75x+x+3 = 0,25x+6
Explications étape par étape
